Telephone-exchange system.



C. W. KECKLER.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED JAN. 2. 1918.

1,294,1 1-1 Patented Feb. 11, 1919.

Char/e6 l L/ Keck/er nn snares Parana" onnrcn.

CHARLES W. KECKLER, OF NEWARK, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Specification of Letters Patent.

Patented Feb. 11, 1919.

Application filed January 2, 1918. Serial No. 209,971.

tening keys.

In such systems, it is desirable to prevent the operator from listening in on established connections.

It is the object of this invention to provide a simple and inexpensive system of this character in which the operator is absolutely prevented from simultaneously listening to the conversations being communicated over two or more of the telephone lines.

In accordance with a feature of this in vention, the listening keys of the link or connecting circuits assigned to an operator are so interconnected that the operators telephone set is rendered ineffective upon any attempt being made to contemporaneously connect the operators telephone set with two or more subscribers lines.

This and other features not specifically mentioned, will more fully appear from the following description and the annexed drawing illustrating one embodiment of the in vention.

In the accompanying drawing, the figure shows two ordinary subscribers lines A and B terminating at a central office at which several link or connecting circuits C, D and E, having listening keys 10, 20 and 30, respectively, are provided for interconnecting such lines.v For the sake of clearness, only such portions of the connecting circuits are shown as are essential to a complete understanding of the invention and although only the listening keys and their associated connections are shownfor cord circuits C and E, it may be assumed that such circuits are similar to the one shown for cord circuit D.

The bus or common conductors 4 and 5 connected with the operators telephone circuit are multiplied at each of the keys 10, 20 and 30 and connection with any link circuit may be established by the closure of the normally open contacts 11 and 17, 21 and 27 or 31 and 37 of the associated listening key. The normally closed contacts 14, 24 and 34 of the listening keys 10, 20 and 30, respectively, are connected in scrz'atim by means of conductors 7 and 6, thereby forming a normally continuous common conductor joining all of the listening keys.

It is thought that the invention may be more fully understod from the following description of the operation of the system.

Assuming that the subscriber at line A desires to converse with the subscriber on line B, the signal of line A is displayed in the usual manner and the operator inserts plug 1 of cord circuit D in the jack of line A and actuates listening key 20. The actuation of this key connects the operators telephone set conductors 4 and 5 with the tip and ring conductors respectively, of the answering portion of the cord circuit D by the closure of contacts 21 and 27. At the same time, the tip conductor of the cord' circuit is opened at contact 22 of key 20 and the calling end of the cord circuit D is short-circuited by. means of a connection from the tip of the cord through contacts 26 and 27 to the ring of the cord. After ascertaining that a connection with line B is desired, the operator inserts plug 2 in the jack of line B and restores the listening key 20 so that subscribers A and B may then converse after subscriber B has been signaled in the usual manner.

It will be noted, however, that in case listening key 20 is actuated at any time the calling end of the cord circuit is short-circuited as before, thus preventing the operator from listening in on the conversation conducted over that cord circuit.

In case the operator should actuate key 10 of the cord circuit C before key 20 is restored, the bus conductors 4 and 5 will be short-circuited by a circuit extending from conductor 4 through contact 23 of key 20,.

key 20, conductor 6, contact. 33 of key 30 to conductor 4:.

It will be evident that no manipulation of thecord circuits and their associated apparatus will enable the operator to simultaneously listen to conversations on two or more of the lines.

What is claimed is:

l. A telephone exchange system comprising a. plurality of telephone lines terminating at a central ofiice, a plurality of link circuits for interconnecting the lines, an operators telephone set, a listening key for each link circuit for connecting the operators telephone set therewith, a normally closed contact for each key, a plurality of additional contacts for each key, and a common circuit conductor interconnecting the normally closed contacts and cooperating with the additional contacts to shortcircuit the operators telephone set when two of the listening keys are actuated.

2. A telephone exchange system comprising a plurality of telephone lines terminating at a central oflice, a plurality of link circuits for interconnecting the lines, an operators telephone set, a listening key for each link circuit for connecting the operators telephone set therewith, a common conductor interconnecting the keys, means associated with each listening key for interrupting the common conductor, and additional means associated with the listening keys and cooperating with the interrupting means to short-circuit the operators telephone circuit when any two of the keys are actuated.

3. A telephone exchange system compris- I ing a plurality of "telephone lines terminating at a central office, a plurality of link circuits for interconnecting the lines, an operators telephone set, a listenlng key for each link circuit for connecting the operat'ors telephone set therewith, a common conductor interconnecting the keys, means associated with the listening keys to sect-ionalize the portion of the common conductor connecting any two of the keys upon the operation of said two keys, and additional means associated with said two keys and cooperating with said section of common conductor to short-circuit the operators telephone set. V 1

4. A telephoneeXcha-nge system comprising a plurality of telephone lines terminating at a central office, a plurality of link circuits for interconnecting the lines, an operators telephone set, a listening key for each link circuit for connecting the operators set therewith, and means for preventing the contemporaneous connection of the telephone set with a plurality of the link circuits, said means consisting of a short circuit for the telephone set established solely by the cooperation of contacts of the listening keys and circuit connections therefor. V p

5. A telephone exchange "system comprising a plurality of telephone lines terminating at a central oiiice, a plurality of link circuits for interconnecting the lines, an operators telephone set, a listening key for each link circuit for connecting the operators set therewith, and means for prevent ing the operator from simultaneously listening in on a plurality of the link circuits, said means consisting of a short circuit for the operators set established solely by the operation of contacts on the keys and cir-' cuit interconnections therefor.

In Witness whereof, I hereunto subscribe Copies of this patent may be obtained for five cents each, by addressing the Commissioner of ;Patex'1ts,'

Washington, D. G. 

